Pallets are conventionally used to ship various types of goods. Placing a load of goods on a pallet, particularly if tied down and attached securely to the pallet, allows the load to be handled efficiently using vehicles or devices having manipulators adapted to fit into or under the pallet, such as the tines of a fork lift. This affords protection for the goods. Handling stresses are borne by the pallet. There is substantial efficiency in handling the goods as a unit load larger than cartons or other components in the load. The pallet is a standardized platform on which odd shaped goods may be carried. Pallets can be associated with structural spacers for stacking.
Some of the same advantages enjoyed when using pallets have led to the development and widespread adoption of intermodal containers. Intermodal containers can accommodate multiple pallet loads, providing the ability to handle an even larger load as a unit. Intermodal containers also provide standardization of sizes. More capable manipulators can be used in addition to fork trucks. The containers are typically closed boxes that can be stacked. The containers can be connected to one another, for example by corner couplings for stacking in registry, and also for fitting standardized berths on ships, truck and rail chassis and the like.
Containers offer superior protection for their contents. The container and its load are readily transferred between different modes of transport, e.g., road, rail or ship, carrying along the protection and convenience, without the need to open the container unless the load is to be broken. Large ocean-going vessels have been designed for handling the containers which can be stacked one on top of the other perhaps as many as seven high, with the container framing carrying the weight of the contents of the stack. The standard width of ISO containers is 8 feet (2.44 m), the standard heights are 8 feet 6 inches (2.59 m), and 9 feet 6 inches (2.9 m), and the most common lengths are 20 feet (6.1 m) and 40 feet (12.19 m). The containers are also manufactured in a number of different lengths from 24 feet (7.31 m) to 56 feet (17.22 m). The 20 foot length is a common variety, internally about 6 m long by 2.4 m wide.
Containers are often regarded as appropriate for loads comprising smaller packages such as cartons. Some products involve relatively large and/or heavy units and are sometimes transported as bulk loads, rather than in containers. However, transport of such loads in containers, if possible, can have distinct advantages.
One type of product that is still frequently transported as a bulk load on board ship is steel coil. These coils comprise elongated sheet metal strips in various widths weighing up to 25,000 kg. The coils are stored in dockside warehouses on the order of 20,000,000 to 50,000,000 kg storage capacity. Sufficient warehouse capacity is needed to accumulate and dispense stock so as to smooth over time variations between the demand for steel coils and periodic shipments. If regular supplies could be established, less warehouse capacity might be sufficient.
Transportation of bulk cargo such as steel coils, may expose the cargo to potential damage. Mechanical damage can result if a coil is struck or dropped. Environmental damage can occur, for example from exposure to the elements, such as sea water. Resting a coil on a flat surface or stacking a coil in a nested stack can cause deformation. Resting the coils on the ground or on a wet or dusty surface can introduce unwanted dirt, and can damage the coils when stones or uneven surfaces are beneath the coil. Often the sheet coil material has been provided with a surface treatment at some expense, such as a surface coating of organic paint or another finish. Such a coating or finish advantageously should be protected against damage. For bulk coil cargo, problems of exposure and the like have led to encapsulation of the coils in protective packaging. Many of these problems might be avoided if the coils could be transported in containers. But there are problems. One problem results from the fact that the coils can be very heavy and their weight is densely concentrated.
Standard intermodal containers may be structured to carry substantial weight, but typically the weight is distributed evenly over the available floor area of the container in laterally abutting units such as palleted cartons. Assuming that a dense and heavy weight such as a sheet metal coil is mounted on a pallet, all the weight of the coil is applied to the area encompassed by the pallet. This weight may be too concentrated. Assuming a container is designed, for example, to carry up to 30,000 kg, that weight is expected to be distributed over the floor and not applied to only a small area of the container floor. A typical steel coil, weighing 7,000 kg or more, carried on a typical pallet, may exceed a container's design capacity as to weight concentration. If a coil is a lone weight on a pallet and/or if the pallet is a small item in a container, of whatever weight, dynamic loads imposed during transportation at sea may cause the weight to move, and develop inertial force that is more than the container structure can bear.
The coils can be carried on pallets that are sized to occupy an area of the container, wherein the area occupied is proportional to the weight of the coils to be carried, and perhaps also encompasses the corresponding proportionate area of the container. In that case (and assuming that the pallets are weighty as well), the standard 30,000 kg capacity shipping container might carry three 7,000 kg coils, each on a structure occupying a third of the floor space, or two 13,000 kg coils, each occupying half, or one 25,000 kg coil on a structural reinforcing pallet that distributes the weight over the whole area.
Such a technique is exemplified by U.S. Pat. No. 6,231,284—Kordel. According to that patent and the products available currently from Coil-Tainer Ltd., West Chester, Pa., large pallets that occupy the full width of standard shipping containers are designed to handle very heavy cylindrical loads such as steel coil. The pallets are considered “modular” in that pallets are proportionately sized to distribute the weight of coils over integral lengths of the container. For example, a container can be filled with two half-length pallets, four quarter-length pallets or two quarter-length and one half length pallet. Empty pallets can be used to take up space and lock in load-bearing pallets in a partially-full container.
The pallets disclosed in Kordel thus help to solve problems associated with weight distribution and permit the use of intermodal type containers to carry dense heavy weights such as sheet metal coils. However, this system relies on having a range of pallet sizes (or at least two distinct pallet sizes), and that has introduced logistical difficulties and inefficiencies. Often, larger and heavier steel coil is routinely shipped to a given destination for processing in the production of products. Smaller and lighter processed steel coil is more likely to be shipped out from that location than large coils. As a result, large pallets accumulate at that destination and there is an insufficient supply of smaller pallets.
In the foregoing scenario, it is possible to use the extra large pallets (e.g., half-container-length) pallets to ship out smaller coils (e.g., coils that could be carried in a quarter of the container capacity instead of half). It is also possible to ship a supply of small pallets to the destination, empty, and to ship the large pallets back to the original shipping point, also empty. Either the pallets are under-utilized or the containers are under-utilized, or both.
Known modular pallet arrangements could be effective for distributing the weight of large or small coils or other loads proportionately over the area available in a container. The known technique also could efficiently use available shipping capacity. Due to the lopsided movement and need for large and small pallets, it has not been possible to realize both objectives. There is a need for a palletization system that can better realize the potential to accommodate both large and small steel coils, to use all the shipping capacity that is available in containers as well as the pallets they carry, and at the same time to reduce the need to support the operation by shipping pallets and equipment unloaded or otherwise used to less than their full capacity.